Positive electrode material, positive electrode slurry comprising same, positive electrode, and lithium secondary battery

Abstract

The present invention relates to a positive electrode material for a lithium secondary battery, the positive electrode material for a lithium secondary battery comprising: a first positive electrode active material containing a lithium-rich manganese-based oxide; and a second positive electrode active material containing a lithium transition metal oxide, the second positive electrode active material having one or more particles in the form of a single particle composed of one small block or a quasi-single particle that is a composite of 30 or less small blocks, and containing a lithium transition metal oxide, wherein the first positive electrode active material has a D50 of 8 [mu] m or more and has a value greater than the D50 of the second positive electrode active material, and the present invention relates to a positive electrode paste, a positive electrode, and a lithium secondary battery comprising the same.

Description

Technical Field

[0001] Cross-reference to related applications This application claims priority to Korean Patent Application No. 10-2023-0065296 filed on May 19, 2023 and Korean Patent Application No. 10-2024-0052072 filed on April 18, 2024, the disclosures of which are incorporated herein by reference in their entirety.

[0002] The present invention relates to a cathode material and cathode slurry, cathode and lithium secondary battery comprising the cathode material and thereby having improved physical properties, the cathode material comprising: lithium-rich manganese oxides having a D50 value above a certain level as large particles, and lithium transition metal oxides in the form of single particles or quasi-single particles as small particles. Background Technology

[0003] In recent years, as the application fields of lithium secondary batteries have rapidly expanded not only to power sources for electronic devices such as electrical, electronic, communication and computer devices, but also to power storage and supply for large-area devices such as automobiles and power storage systems, the demand for secondary batteries with high capacity, high output and high stability has been increasing.

[0004] Lithium-ion rechargeable batteries typically consist of a positive electrode containing a positive active material, a negative electrode containing a negative active material, an electrolyte serving as the lithium-ion transport medium, and a separator. Carbon-based or silicon-based active materials can be used as the negative electrode active material. Furthermore, layered lithium transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium nickel cobalt manganese composite oxides can be used as the positive electrode active material.

[0005] In recent years, lithium-rich manganese oxides have attracted much attention as next-generation cathode active materials. These oxides offer the advantage of high capacity due to the increased content of relatively inexpensive and abundant manganese (Mn). However, a limitation of these lithium-rich manganese oxides is their low rate capability. Therefore, to address this issue, methods have previously been employed to fabricate smaller primary particles to increase the BET specific surface area of ​​the secondary particles. However, when using this method to fabricate cathode active materials with large specific surface areas, another problem may arise: a decrease in the rolling density of the cathode.

[0006] To address these issues, conventional methods have been employed, such as coating the surface of the lithium manganese oxide cathode with metal oxides to enhance surface stability. However, this approach has been shown to have limitations, including a further reduction in rate performance. Summary of the Invention

[0007] Technical issues One object of the present invention is to provide a positive electrode material for lithium secondary batteries, wherein the positive electrode material for lithium secondary batteries enhances electrode density and particle durability by incorporating small particle positive electrode active material in the form of single particles when introducing lithium-rich manganese oxides as positive electrode materials.

[0008] Another object of the present invention is to provide a positive electrode slurry for lithium secondary batteries, which has an increased solids content while maintaining appropriate viscosity by including the positive electrode material as described above.

[0009] Another object of the present invention is to provide a positive electrode and a lithium secondary battery, wherein the positive electrode and the lithium secondary battery have improved life and resistance characteristics by applying the above-mentioned positive electrode material.

[0010] Technical solution According to one embodiment, a positive electrode material for a lithium secondary battery is provided, the positive electrode material for the lithium secondary battery comprising: The first positive electrode active material contains a lithium-rich manganese oxide represented by the following chemical formula 1; and The second positive electrode active material has one or more particles and contains lithium transition metal oxide, wherein the particles are in the form of single particles consisting of a nodule or quasi-single particles as a composite of 30 or fewer nodules. The first positive electrode active material has a D50 of more than 8 μm and a larger D50 value than the second positive electrode active material. [Chemical Formula 1] Li 1+a [Mn 1-(b+c) Ni b M c ]O 2+d In chemical formula 1, M is selected from at least one of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.10≤a≤0.45, 0≤b≤0.5, 0≤c≤0.5, 0 <b+c≤0.5,0≤d≤1。

[0011] According to another embodiment, a positive electrode slurry for lithium secondary batteries is provided, the positive electrode slurry for lithium secondary batteries comprising: a positive electrode material, a binder, a conductive material, and a solvent.

[0012] According to another embodiment, a positive electrode for a lithium secondary battery is provided, the positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer disposed on the positive electrode current collector and comprising a positive electrode material. The cathode material comprises: a first cathode active material containing a lithium-rich manganese oxide represented by chemical formula 1; and a second cathode active material having one or more particles and containing a lithium transition metal oxide, wherein the particles are in the form of single particles composed of small pieces or quasi-single particles as a composite of fewer than 30 small pieces. The first positive electrode active material has a D50 of more than 8 μm and has a larger D50 value than the second positive electrode active material.

[0013] According to another embodiment, a lithium secondary battery comprising the positive electrode is provided.

[0014] Beneficial effects Because the cathode material for lithium secondary batteries according to the present invention contains lithium-rich manganese oxides, it has high capacity and is more competitive in terms of raw material supply and price than conventional cathode active materials containing relatively high amounts of nickel or cobalt.

[0015] Furthermore, by mixing with small-particle-size cathode active materials that are essentially single-particle in form, the limitations of conventional lithium-rich manganese oxides can be overcome, such as the decrease in cathode rolling density or manufacturing process efficiency due to the high BET specific surface area.

[0016] Specifically, because the cathode material according to the present invention can achieve a higher solids content slurry at the same viscosity compared to conventional cathode materials containing only secondary particles, it is advantageous to reduce the coating thickness in the electrode manufacturing process, thus making it easier to control subsequent calendering processes. Therefore, it is possible to provide a cathode with higher density while experiencing less particle breakage due to the calendering process. Attached Figure Description

[0017] Figure 1 A graph showing the PSD (volume cumulative particle size distribution) analysis results of the powder containing the cathode material before and after calendering for the cathode material manufactured in Example 4; Figure 2 A graph showing the PSD analysis results of the powder containing the cathode material before and after calendering for the cathode material manufactured in Comparative Example 2; Figure 3 A graph showing the change in porosity of the positive electrode active material layer with the number of calendering cycles when manufacturing a positive electrode containing the positive electrode materials manufactured in Example 4 and Comparative Example 2; Figure 4A graph showing the measurement results of the rheological properties of the cathode slurry containing the cathode materials manufactured in Example 4 and Comparative Example 2; Figure 5 The images are scanning electron microscope images of the positive electrode active material A used in the examples and comparative examples. Figure 6 Scanning electron microscope images of the positive electrode active material C used in the examples and comparative examples; Figure 7 The images are scanning electron microscope images of the positive electrode active material D used in the examples and comparative examples; and Figure 8 The images show scanning electron microscope (SEM) images of the particle cross-sections of the positive electrode active material A used in the examples and comparative examples. Detailed Implementation

[0018] The specific embodiments of the present invention will now be described in more detail.

[0019] As used herein, “single particle” refers to a particle consisting of a single piece, and “quasi-single particle” refers to a particle that is a composite of fewer than 30 pieces. However, unless otherwise specified herein, “single particle” should be considered a general term that includes “quasi-single particle” types.

[0020] As used in this article, "primary particle" refers to a particle that does not appear to have grain boundaries when observed with a scanning electron microscope at a magnification of 5,000 to 20,000 times, and "secondary particle" refers to a particle formed by the aggregation of multiple primary particles.

[0021] As used in this article, “nodule” refers to a block of particle units that constitute single particles and quasi-single particles, and a nodule is a single crystal lacking any crystal boundaries, or it can be a polycrystalline material that does not show grain boundaries when observed with a scanning electron microscope (SEM) at a field of view of 5,000 to 20,000 times.

[0022] As used herein, "mean primary particle size" refers to the arithmetic mean calculated after measuring the particle size of at least 20 primary particles observed from scanning electron microscope images. In this context, particle size refers to the diameter of the largest major axis of the primary particle.

[0023] As used herein, "D50" refers to the particle size corresponding to 50% of the volumetric cumulative particle size distribution of the powder under test, and can be measured by laser diffraction. For example, positive electrode active material powder is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S-3500) to be irradiated with ultrasound at approximately 28 kHz to an output of 60 W. It can then be measured by obtaining the volumetric cumulative particle size distribution curve and then determining the particle size at 50% of the volumetric cumulative amount.

[0024] As used in this paper, the “BET surface area” is measured by the BET (Brunauer-Emmett-Teller) method, specifically, it can be calculated from the nitrogen adsorption isotherm obtained using BELSORP-MAX (MicrotracBEL Corp.) in a liquid nitrogen atmosphere at 77 K.

[0025] Furthermore, in the following chemical formulas 1, 1a, 2 and 3, the subscript characters contained in each chemical formula indicate the molar ratio of each element.

[0026] cathode materials According to one embodiment of the present invention, a positive electrode material for a lithium secondary battery is provided, the positive electrode material for a lithium secondary battery comprising: The first positive electrode active material contains a lithium-rich manganese oxide represented by the following chemical formula 1; and The second positive electrode active material has one or more particles and contains lithium transition metal oxide, wherein the particles are in the form of single particles composed of small pieces or quasi-single particles as a composite of fewer than 30 small pieces. The first positive electrode active material has a D50 of more than 8 μm and a larger D50 value than the second positive electrode active material. [Chemical Formula 1] Li 1+a [Mn 1-(b+c) Ni b M c ]O 2+d In chemical formula 1, M is selected from at least one of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.10≤a≤0.45, 0≤b≤0.5, 0≤c≤0.5, 0 <b+c≤0.5,0≤d≤1。

[0027] In cathode materials, lithium-rich manganese oxides contain manganese at a content of 50 mol% or more of all metals except lithium, and can contain lithium in an excess molar ratio defined as 1+a. Due to this high content of lithium and manganese, lithium-rich manganese oxides can have a two-phase crystal structure in which rock salt phase and layered phase are mixed, and in particular, can contain a specific proportion or higher of rock salt phase. Due to the further activation of this rock salt phase, lithium-rich manganese oxides can have higher capacity and energy density than conventional layered cathode active materials such as currently commercialized lithium nickel cobalt manganese (NCM) active materials. In addition, it has the advantage of significantly reducing or essentially eliminating the amount of cobalt contained in the cathode material, thereby reducing manufacturing costs.

[0028] However, because the redox reactions of oxygen and Mn ions proceed relatively slowly, lithium-rich manganese oxides with high manganese content suffer from high electrical resistance and low rate performance. Therefore, improvements are needed to address these issues in order to commercialize lithium-ion secondary batteries using lithium-rich manganese oxides as cathode materials.

[0029] Conventionally, to improve these aspects, the method of reducing the (average) particle size of primary particles to increase the BET specific surface area of ​​secondary particles has been applied. However, when this method is applied, it may cause other problems, such as increased slurry viscosity, decreased electrode processability, particle breakage during the calendering process, and decreased cathode density after calendering.

[0030] Therefore, the inventors mixed and used lithium-rich manganese oxides with single-particle active materials, adjusting the D50 of both the lithium-rich manganese oxides and the single-particle active materials to a specific range. As a result, it was confirmed that the slurry viscosity could be reduced and the solids content increased while simultaneously increasing the total specific surface area of ​​the cathode material and suppressing the increase in resistance. This resulted in a reduced slurry coating thickness, making it easier to dry, and achieving the target thickness with lower pressure during the calendering process, which also reduced the stress applied to the cathode material.

[0031] On the other hand, lithium-rich manganese oxides have a larger BET specific surface area compared to NCM-type active materials, and the presence of internal voids due to their secondary particle shape limits their ability to achieve low electrode densities and increases particle breakage during rolling. For example, Figure 8 The image shows a SEM image of the cross-section of the positive electrode active material A used in the embodiments described later. This image confirms the formation of large voids within the lithium-rich manganese oxide particles. However, when using the positive electrode material of one embodiment, as described above, the calendering process is easily controlled. Therefore, not only can particle breakage during calendering be suppressed, but a higher density positive electrode can also be provided after calendering.

[0032] In one embodiment of the invention, the cathode material can exhibit a bimodal particle size distribution overall because the particle size distributions of the first cathode active material (large particles) and the second cathode active material (small particles) are different from each other. In this case, since the small particles fill the gaps between the large particles during electrode rolling, there is an advantage of increased electrode density and the ability to achieve high energy density.

[0033] On the other hand, in Formula 1, 'a' represents the excess molar ratio of Li in the lithium-rich manganese oxide, where 'a' in Formula 1 can satisfy 0.10 ≤ a ≤ 0.45, 0.15 ≤ a ≤ 0.4, or 0.20 ≤ a ≤ 0.38. If 'a' meets these ranges, high capacity can be achieved. Conversely, if the value of 'a' is too small, high capacity becomes difficult to achieve due to factors such as activation of the rock salt phase. If the value of 'a' is too large, the crystal structure of the lithium-rich manganese oxide itself may become unstable, or side reactions may increase significantly.

[0034] In addition, b is the molar ratio of Ni in lithium-rich manganese oxides, where b in chemical formula 1 can satisfy 0≤b<0.5 or 0.1≤b≤0.45 or 0.3≤b≤0.4.

[0035] c represents the molar ratio of the additional element M in the lithium-rich manganese oxide. In chemical formula 1, c can be 0 ≤ c < 0.5, 0 ≤ c ≤ 0.2, 0 ≤ c ≤ 0.1, or 0 ≤ c ≤ 0.05. In this case, the additional element M is an element that forms the crystal structure of the lithium-rich manganese oxide, or it can be a doping element or coating element on the lithium-rich manganese oxide. If M is an additional element that forms the crystal structure of the lithium-rich manganese oxide, then M may not include cobalt. This stabilizes the two-phase crystal structure of the lithium-rich manganese oxide, thereby exhibiting high capacity characteristics and reducing the manufacturing cost.

[0036] However, even if cobalt is not included in the elements forming the crystal structure of lithium-rich manganese oxides, it can be added as a dopant or coating element to the lithium-rich manganese oxides, and even in this case, it can still be included in the category of lithium-rich manganese oxides that are essentially cobalt-free. In this case, the cobalt content can satisfy a ratio of c ≤ 0.1 or 0 ≤ c ≤ 0.05.

[0037] On the other hand, if the content of the additional element M is too high, it will not only have an adverse effect on the capacity of the active material, but will also exacerbate the gas generation and degradation of the positive electrode active material during the redox reaction of oxygen, thus leading to a decrease in lifetime characteristics.

[0038] 1 - (b + c) is the molar ratio of Mn in the lithium - rich manganese - based oxide, where b and c in Chemical Formula 1 can satisfy 0 < b + c ≤ 0.5 or 0 < b + c < 0.5 or 0.1 ≤ b + c ≤ 0.45 or 0.3 ≤ b + c ≤ 0.4. In particular, since the molar ratio of Mn contained is greater than the molar ratio of other metals except lithium, for example, it satisfies a range such as 0.55 ≤ 1 - (b + c), the lithium - rich manganese - based oxide can contain a sufficient rock - salt phase. Thus, excellent capacity expression of the lithium - rich manganese - based oxide can be achieved, and the stability of the crystal structure can be ensured.

[0039] 2 + d is the molar ratio of oxygen in the lithium - rich manganese - based oxide, where d in Chemical Formula 1 can satisfy 0 ≤ d ≤ 0.5, 0 ≤ d ≤ 0.45 or 0 ≤ d ≤ 0.4.

[0040] On the other hand, in the lithium - rich manganese - based oxide represented by Chemical Formula 1, the ratio of the number of moles of Li to the number of moles of all metal elements except Li (Li / Me) can be, for example, 1.10 to 1.45, or 1.15 to 1.4, or 1.20 to 1.38. If the Li / Me ratio satisfies the above range, the rate performance and capacity characteristics are excellent. If the Li / Me ratio is too high, the conductivity may decrease and the rock - salt phase (Li2MnO3) may increase, which may increase the degradation rate. If the Li / Me ratio is too low, the improvement effect on the energy density is small.

[0041] On the other hand, when the lithium - rich manganese - based oxide contains too much lithium, it has a crystal structure in which the layered phase (LiM'O2) and the rock - salt phase (Li2MnO3) are mixed. The two - phase crystal structure of the lithium - rich manganese - based oxide can be represented by the following Chemical Formula 1a. Because of the two - phase crystal structure in which the rock - salt phase is mixed in a specific proportion or more in this way, the lithium - rich manganese - based oxide can be clearly distinguished from the existing layered - structure cathode active material, and can exhibit a high capacity and energy density even when the contents of nickel and cobalt are low.

[0042] [Chemical Formula 1a] A·Li2MnO3·(1 - A)·Li[Ni 1-n-m Mn n M m O2 Wherein in Chemical Formula 1a, M includes at least one selected from Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.10 ≤ A ≤ 0.45, 0.4 ≤ n < 1, 0 ≤ m ≤ 0.2.

[0043] A refers to the proportion of rock salt phase (Li2MnO3 phase) in lithium-rich manganese oxides, and n and m refer to the molar ratio of Mn to additional element M on the LiM'O2 layer, which can also be converted from the content ratio of various metal elements in the above chemical formula 1.

[0044] On the other hand, if desired, a coating can be included on the surface of the lithium-rich manganese oxide. In this case, the coating inhibits contact between the lithium-rich manganese oxide and the electrolyte, which can reduce side reactions of the electrolyte and improve the battery's lifespan characteristics.

[0045] The coating may include coating element M 1 The coating element M 1 It can be, for example, at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr. In a specific example, M 1 It can be Al, Co, Nb, W, or combinations thereof; in a more specific instance, it can be Al, Co, or combinations thereof. Coating element M 1 It can contain more than two types, such as Al and Co.

[0046] Coating elements can exist in the coating in the form of oxides, i.e., M 1 O z (1≤z≤4).

[0047] Coatings can be formed using methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). Among these, coatings can be formed using atomic layer deposition because it allows for the formation of large-area coatings.

[0048] Based on the total surface area of ​​the lithium-rich manganese oxide particles, the coating formation area can be 10% to 100%, 30% to 100%, or 50% to 100%. When the coating formation area meets the above ranges, the effect of improving lifetime characteristics is excellent.

[0049] On the other hand, the lithium transition metal oxide contained in the second positive electrode active material can be represented by the following chemical formula 2 or chemical formula 3.

[0050] [Chemical Formula 2] Li 1+p (Ni q Co r Mn s M 2 t O2 In chemical formula 2, M 2comprising at least one selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and -0.2 ≤ p ≤ 0.2, 0.50 ≤ q < 1, 0 < r ≤ 0.40, 0 < s ≤ 0.40, 0 ≤ t ≤ 0.10, q + r + s + t = 1, [Chemical Formula 3] Li 1+w [Mn 1-(x+y) Ni x M 3 y O 2+z wherein in Chemical Formula 3, M 3 comprises at least one selected from Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0 < w, 0 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.5, 0 < x + y ≤ 0.5, 0 ≤ z ≤ 1.

[0051] In one example, the lithium transition metal oxide contained in the second positive electrode active material is represented by Chemical Formula 2, wherein q, r, s, and t may respectively satisfy 0.60 ≤ q < 1, 0 < r ≤ 0.30, 0 < s ≤ 0.30, and 0 ≤ t ≤ 0.10. That is, the lithium transition metal oxide contained in the second positive electrode active material may be a lithium nickel cobalt manganese oxide in which the content of nickel in the transition metal is 60 mol% or more.

[0052] 1 + p represents the molar ratio of lithium in the lithium nickel cobalt manganese oxide, wherein -0.2 ≤ p ≤ 0.2, or -0.1 ≤ p ≤ 0.2, or 0 ≤ p ≤ 0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel cobalt manganese oxide can be stably formed.

[0053] q represents the molar ratio of nickel in all metals other than lithium in the lithium nickel cobalt manganese oxide, wherein 0.50 ≤ q < 1, or 0.60 ≤ q < 1, or 0.70 ≤ q < 1, or 0.80 ≤ q < 1, or 0.85 ≤ q < 1. When the molar ratio of nickel satisfies the above range, it exhibits a high energy density and can achieve a high capacity.

[0054] r represents the molar ratio of cobalt in all metals other than lithium in the lithium nickel cobalt manganese oxide, wherein 0 < r ≤ 0.40, or 0 < r ≤ 0.30, or 0 < r ≤ 0.20, or 0 < r ≤ 0.15, or 0 < r ≤ 0.10. When the molar ratio of cobalt satisfies the above range, it can achieve excellent resistance characteristics and output characteristics.

[0055] s represents the molar ratio of manganese among all metals other than lithium in the lithium nickel cobalt manganese oxide, where 0 < s ≤ 0.40, or 0 < s ≤ 0.30, or 0 < s ≤ 0.20, or 0 < s ≤ 0.15, or 0 < s ≤ 0.10. When the molar ratio of manganese satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0056] In a specific embodiment of the positive electrode material, the lithium nickel cobalt manganese oxide represented by Chemical Formula 2 may include at least one additional element selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and in this case, structure degradation can be suppressed and improved high-temperature durability can be exhibited. In a specific example, the lithium nickel cobalt manganese oxide represented by Chemical Formula 2 may contain Al as an additional element. Further, t representing the molar ratio of the additional element among all metals other than lithium in the lithium nickel cobalt manganese oxide may be 0 ≤ t ≤ 0.10, or 0 ≤ t ≤ 0.08, or 0 ≤ t ≤ 0.06, or 0 ≤ t ≤ 0.05.

[0057] On the other hand, when the lithium transition metal oxide contained in the second positive electrode active material is a compound represented by Chemical Formula 3, the description regarding the lithium-rich manganese oxide of the first positive electrode active material can be similarly applied.

[0058] For example, in Chemical Formula 3, w may satisfy 0 < w, or 0.10 ≤ w ≤ 0.45, or 0.15 ≤ w ≤ 0.40, or 0.2 ≤ w ≤ 0.38, x may satisfy 0 ≤ x < 0.5, or 0.1 ≤ x ≤ 0.45, or 0.3 ≤ x ≤ 0.4, and y may satisfy 0 ≤ y < 0.5, or 0 ≤ y ≤ 0.2, or 0 ≤ y ≤ 0.1, or 0 ≤ y ≤ 0.05.

[0059] Further, 1 - (x + y) is the molar ratio of Mn in the compound represented by Chemical Formula 3, which can satisfy 0 < x + y ≤ 0.5, or 0 < x + y < 0.5, or 0.1 ≤ x + y ≤ 0.45, or 0.3 ≤ x + y ≤ 0.4, and z may satisfy 0 ≤ z ≤ 1, or 0 ≤ z ≤ 0.5, or 0 ≤ z ≤ 0.45, or 0 ≤ z ≤ 0.4.

[0060] In one specific embodiment, the cathode material may comprise a first cathode active material and a second cathode active material in a ratio of 50:50 to 90:10, 50:50 to 80:20, 60:40 to 70:30, or 60:40 to 65:35. When the weight ratio of the first cathode active material to the second cathode active material is within the above range, not only can the filling density be increased while appropriately filling the space between large particles with small particles, but the rolling stress during the rolling process can also be alleviated.

[0061] On the other hand, the first positive electrode active material can be composed of secondary particles formed by the aggregation of multiple primary particles, and based on the secondary particles, the D50 of the first positive electrode active material can be greater than 8 μm, or 8 μm to 15 μm, or 8 μm to 12 μm. When the D50 of the first positive electrode active material is less than 8 μm, the difference in particle size between it and the second positive electrode active material becomes smaller, which may make it difficult to fully realize the effect of improving the filling density brought about by the bimodal configuration.

[0062] Furthermore, the BET specific surface area of ​​the first positive electrode active material can be 1.3 m². 2 / g or more, or 1.5 m 2 A specific surface area of ​​4.0 m² / g or higher can achieve high capacity and efficiency. However, considering the issues of electrode processability, large surface area, and increased surface side reactions and inhomogeneities due to low sphericity, the BET specific surface area can be limited to 4.0 m² / g. 2 / g or less, or 3.0 m 2 / g or less.

[0063] Furthermore, the D50 of the second positive electrode active material can be from 2 μm to 5 μm, or from 2.5 μm to 4.5 μm, and the BET specific surface area of ​​the second positive electrode active material can be 0.5 m². 2 / g to 1.2 m 2 / g. Due to the D50 of the second positive electrode active material, the gaps between the particles of the first positive electrode active material are effectively filled, reducing particle breakage during calendering and enabling the provision of a higher density positive electrode after calendering.

[0064] On the other hand, in the cathode material according to one embodiment described above, the particle breakage rate of the first cathode active material according to the following mathematical formula 1 can be less than 20%, or 0% to 18%, or 3% to 15%: [Mathematical Expression 1] The particle fragmentation rate (%) of the first positive electrode active material = the particle distribution ratio at the maximum peak obtained from the PSD (volume cumulative particle size distribution) of the positive electrode material before rolling (%) - the particle distribution ratio at the maximum peak obtained from the PSD of the positive electrode material after rolling (%) In mathematical formula 1, The PSD of the cathode material before calendering refers to the powder obtained by drying and pulverizing a cathode slurry containing cathode material. The PSD of calendered cathode material refers to the PSD of cathode material powder recovered from a cathode containing cathode material and having a porosity of less than 30%.

[0065] Positive electrode slurry Next, the cathode slurry containing the cathode material according to one embodiment will be described.

[0066] The positive electrode slurry comprises a positive electrode material, a binder, a conductive material, and a solvent according to one of the above embodiments.

[0067] In one specific embodiment, the solids content of the cathode slurry can be 65% by weight or more relative to the total weight of the cathode slurry, and the viscosity is 14,500 cP or less. In other words, this means that by including the above-mentioned cathode material, the solids content can be maintained at a certain level without excessively increasing the viscosity, thereby ensuring the capacity and processability of the cathode. Here, the solids content is measured by drying the cathode slurry in an oven to remove all solvent and measuring the remaining weight, and the viscosity is measured at 25°C using a Brookfield DV2T LV TJ0 viscometer with rotor 64 (LV-03) at 12 rpm.

[0068] Specifically, the solids content in the positive electrode slurry can be 66% by weight or more, 67% by weight or more, or 68% by weight or more. From the perspective of suppressing binder migration and improving electrode productivity, a higher solids content in the slurry is preferred. In the case of dry electrodes, the solids content can be 100% by weight, but when using solvents, it can be 85% by weight or less to prevent the viscosity from becoming too high. On the other hand, considering the ease of slurry delivery and coating processability, the viscosity of the positive electrode slurry can be 14,000 cP or less, or 13,000 cP or less, or 12,000 cP or less. However, when considering slurry precipitation and phase stability, it can be 5,000 cP or more, more specifically 8,000 cP or more.

[0069] On the other hand, based on the total weight of solids in the cathode slurry, the content of the cathode active material can be from 90% to 99% by weight, specifically from 95% to 99% by weight, and more specifically from 97% to 98% by weight. If the content of the cathode active material in the solids is less than 90% by weight, the energy density may be lower and the capacity may be reduced.

[0070] On the other hand, the adhesive may include any one or more of the following substances: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber and various copolymers thereof, specifically, it may include polyvinylidene fluoride (PVDF).

[0071] Based on the total weight of solids in the cathode slurry, the binder content can be from 0.5% to 2.5% by weight, or from 1% to 2% by weight, or from 1.5% to 2% by weight. When the binder content is within the above range, it can adequately ensure adhesion to the current collector and bonding between particles, and can maintain a low initial resistance while improving cathode durability.

[0072] The conductive material can be selected from one or more of the following: graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; carbon materials such as carbon fibers and carbon nanotubes; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. More specifically, the conductive material can be carbon nanotubes or carbon black.

[0073] Based on the total weight of solids in the cathode slurry, the content of conductive material can be from 0.1% to 2.5% by weight, or from 0.3% to 2% by weight, or from 0.5% to 1% by weight. When the content of conductive material is within the above range, it is possible to reduce the dead volume within the active material layer while maintaining the conductivity between active materials.

[0074] In addition, the cathode slurry may optionally contain a dispersant, and the dispersant may be hydrogenated nitrile butadiene rubber (HNBR).

[0075] On the other hand, the solvent for the positive electrode slurry can be a solvent commonly used in this technical field. For example, N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropanol, dimethylformamide (DMF), acetone, water, or a mixture of two or more thereof can be used. The solvent can be used in an amount adjusted to achieve the viscosity of the aforementioned positive electrode slurry.

[0076] positive electrode Next, the cathode material containing one implementation scheme will be described.

[0077] According to another embodiment of the present invention, a positive electrode is provided, the positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer disposed on the positive electrode current collector and comprising a positive electrode material. The cathode material includes: The first positive electrode active material contains a lithium-rich manganese oxide represented by chemical formula 1; and The second positive electrode active material has one or more particles and contains lithium transition metal oxide, wherein the particles are in the form of single particles consisting of a small mass or quasi-single particles as a composite of 30 or fewer small masses. The first positive electrode active material has a D50 of more than 8 μm and has a larger D50 value than the second positive electrode active material.

[0078] In addition, it includes a layer of positive active material formed by coating the aforementioned positive electrode slurry onto at least one surface of the positive electrode current collector.

[0079] Since the cathode material and cathode slurry have already been described above, their detailed descriptions will be omitted, and only the remaining structures will be described in detail below.

[0080] The positive electrode current collector can contain highly conductive metals, and the positive electrode active material layer should adhere easily, but there are no particular limitations as long as it is not reactive within the battery's voltage range. Examples of materials that can be used as the positive electrode current collector include: stainless steel, aluminum, nickel, titanium, calcined carbon; or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc. Positive electrode current collectors typically have a thickness from 3 μm to 500 μm, and can have micro-protrusions formed on their surface to enhance the adhesion of the positive electrode active material. For example, positive electrode current collectors can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabric structures.

[0081] In addition to using the aforementioned cathode materials, the cathode can be manufactured according to conventional cathode manufacturing methods. Specifically, it is manufactured by coating a cathode slurry onto a cathode current collector, followed by drying and calendering, or by casting a cathode slurry onto a separate carrier and then laminating a film layer obtained by peeling it off from the carrier onto the cathode current collector.

[0082] On the other hand, when the positive electrode is pressurized to 7 tons / 1.327 cm at room temperature... 2 The rolling density is 2.9 g / cc or higher, or 2.91 g / cc or higher, or 2.97 g / cc or higher, and less than 3.50 g / cc. As mentioned above, although lithium-rich manganese oxides have high BET specific surface area and porosity, achieving high rolling density in this way can improve energy density.

[0083] In addition, the positive electrode can have 420 mg / 25 cm⁻¹ 2 Up to 540 mg / 25 cm 2 or 440 mg / 25 cm 2 Up to 520 mg / 25 cm 2 or 460 mg / 25 cm 2 Up to 500 mg / 25 cm 2 With a load capacity within the above range, there is an advantage that high energy density can be achieved while appropriately ensuring electrode processability and output.

[0084] Lithium secondary batteries Next, a lithium secondary battery according to yet another embodiment of the present invention will be described.

[0085] A lithium secondary battery specifically includes: a positive electrode, a negative electrode located opposite the positive electrode, a separator between the positive and negative electrodes, and an electrolyte. Since the positive electrode is the same as described above, its detailed description will be omitted, and only the remaining structures will be described in detail below.

[0086] In addition, the lithium secondary battery may optionally include: a battery container housing an electrode assembly that houses the positive electrode, the negative electrode, and the separator; and a sealing member that seals the battery container.

[0087] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material located on the negative electrode current collector.

[0088] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and will not cause chemical changes in the battery. Examples of materials that can be used include: copper, stainless steel, aluminum, nickel, titanium, calcined carbon; copper or stainless steel with surface treatments of carbon, nickel, titanium, silver, etc.; and aluminum-cadmium alloys. Furthermore, negative electrode current collectors can typically have a thickness ranging from 3 μm to 500 μm. Similar to positive electrode current collectors, negative electrode current collectors can also have fine irregularities formed on their surface to enhance the adhesion of the negative electrode active material. For example, negative electrode current collectors can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabric structures.

[0089] The negative electrode active material layer may also optionally include an adhesive and a conductive material together with the negative electrode active material.

[0090] As anode active materials, compounds capable of reversibly inserting and de-intercalating lithium can be used. Specific examples of anode active materials can include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, or amorphous carbon; (semi-metallic) materials capable of forming alloys with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and (semi-metallic) oxides capable of doping and de-doping lithium, such as SiO2. β (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; composites containing (semi-)metallic materials and carbonaceous materials such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of them can be used individually. Furthermore, a thin film of metallic lithium can be used as the negative electrode active material. Moreover, the content of the negative electrode active material can be from 80% to 99% by weight, based on the total weight of the negative electrode active material layer.

[0091] The adhesive is a component that assists in the bonding between the conductive material, the active material, and the current collector, and is added in an amount from 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of adhesives include: polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0092] The conductive material is a component that further improves the conductivity of the negative electrode active material, and its addition amount, based on the total weight of the negative electrode active material layer, can be less than 10% by weight, less than 5% by weight, or from 0.1% to 4% by weight. There are no particular restrictions on this conductive material, as long as it is conductive and does not cause chemical changes in the battery, and it can be, for example: graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal cracking black; conductive fibers such as carbon fiber or metal fiber; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0093] The negative electrode active material layer can be manufactured by coating a negative electrode mixture, prepared by dissolving or dispersing the negative electrode active material and optionally a binder and conductive material in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode mixture onto a separate carrier and then laminating a film layer obtained by peeling it off from the carrier onto the negative electrode current collector.

[0094] On the other hand, in lithium-ion secondary batteries, the separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium-ion secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion movement are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers; or membranes having a laminated structure with two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Additionally, separators coated with ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0095] In addition, the electrolyte used in lithium secondary batteries can be any of the organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that were previously used to manufacture secondary batteries, but is not limited to these.

[0096] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0097] The use of organic solvents is not particularly restricted, as long as they can serve as a medium through which ions participating in the electrochemical reactions of the battery can move. Specifically, organic solvents that can be used include: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic C2 to C20 hydrocarbon group and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are suitable, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant with linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) with low viscosity are preferred, as these mixtures can improve the charge / discharge performance of the battery.

[0098] The use of lithium salts is not particularly restricted, as long as they can provide the lithium ions used in lithium secondary batteries. Specifically, the anions of lithium salts may include at least one selected from the following anions: F - Cl- ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - Specifically, as lithium salts, the following can be used: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. Lithium salts can be used in concentrations ranging from 0.1 M to 4.0 M. When the concentration of the lithium salt is within this range, the electrolyte exhibits suitable conductivity and viscosity, thus demonstrating excellent electrolyte performance, and lithium ions can move efficiently.

[0099] In addition to the electrolyte component, to improve battery life characteristics, suppress battery capacity degradation, and improve battery discharge capacity, the electrolyte may also contain one or more additives, such as: alkylene carbonate halide compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted sulfadiazine ketones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc. In this case, based on the total weight of the electrolyte, the content of additives can be from 0.1 to 5 parts by weight.

[0100] Lithium-ion batteries incorporating the cathode material of one of the above embodiments consistently exhibit excellent discharge capacity, output characteristics, and lifespan characteristics, and are therefore suitable for use in: portable devices such as mobile phones, laptops, and digital cameras; and electric vehicles such as hybrid electric vehicles (HEVs).

[0101] Therefore, according to another embodiment, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0102] The battery module or battery pack can be used as a power source for one or more medium-to-large-sized devices, such as: power tools; electric vehicles, such as electric vehicles (EVs), hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0103] There are no particular restrictions on the external shape of the lithium secondary battery contained in such a module or group, but it can be cylindrical, square, bag-shaped, coin-shaped, etc.

[0104] This type of lithium secondary battery can be used in individual battery cells as power sources for small devices, and it can also be used as a unit battery in medium to large battery modules that contain multiple individual battery cells.

[0105] Examples of medium to large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0106] The present invention will be described in more detail below with reference to specific examples.

[0107] <Example: Manufacturing of Cathode Materials> The positive electrode active materials A to G used in the following examples and comparative examples are commercially available and used, and each has the composition and characteristics shown in Table 1 below.

[0108] [Table 1]

[0109] Example 1 The positive electrode material is manufactured by mixing positive electrode active material A and positive electrode active material E in a weight ratio of 70:30.

[0110] Example 2 The positive electrode material is manufactured by mixing positive electrode active material B and positive electrode active material F in a weight ratio of 65:35.

[0111] Example 3 The positive electrode material is manufactured by mixing positive electrode active material A and positive electrode active material G in a weight ratio of 60:40.

[0112] Example 4 The positive electrode material is manufactured by mixing positive electrode active material A and positive electrode active material G in a weight ratio of 65:35.

[0113] Example 5 The positive electrode material is manufactured by mixing positive electrode active material A and positive electrode active material G in a weight ratio of 70:30.

[0114] Example 6 The positive electrode material is manufactured by mixing positive electrode active material A and positive electrode active material G in a weight ratio of 50:50.

[0115] Example 7 The positive electrode material is manufactured by mixing positive electrode active material A and positive electrode active material G in a weight ratio of 80:20.

[0116] Comparative Example 1 Only positive active material C is used as the positive electrode material.

[0117] Comparative Example 2 The positive electrode material is manufactured by mixing positive electrode active material A and positive electrode active material D in a weight ratio of 65:35.

[0118] Comparative Example 3 The positive electrode material is manufactured by mixing positive electrode active material C and positive electrode active material G in a weight ratio of 65:35.

[0119] <Experimental Example> Experimental Example 1 (1) Preparation of positive electrode slurry Positive electrode slurry was prepared from the positive electrode materials manufactured in the aforementioned examples and comparative examples using the following method.

[0120] First, positive electrode material powder, carbon nanotubes as conductive material, polyvinylidene fluoride as binder, and dispersant containing HNBR were added to N-methylpyrrolidone as solvent in a weight ratio of 97.46:0.62:1.7:0.22, and mixed at 2,500 rpm for 75 minutes using a homogeneous dispersant to prepare positive electrode slurry.

[0121] (2) Measurement of solids content and viscosity of positive electrode slurry Each positive electrode slurry prepared in (1) above was dried in an oven to remove all solvent, and the remaining weight was measured to confirm the solids content. Furthermore, more than 2 / 3 of the volume of each positive electrode slurry was filled into a 250 mL bottle, and the viscosity was measured at 25°C using a Brookfield DV2T LV TJ0 viscometer with rotor 64 (LV-03) at 12 rpm. The measurement results are listed in Table 2 below.

[0122] (3) Measurement of the rheological properties of the positive electrode slurry In the positive electrode slurry prepared in (1) above, the shear viscosity corresponding to the shear rate was measured for the positive electrode slurry containing the positive electrode materials of Example 4 and Comparative Example 2, respectively.

[0123] Specifically, using a rheometer (DHR2) (TA Instrument), 10 mL of each positive electrode slurry was placed in a concentric cylinder within the apparatus, and the shear viscosity was measured while gradually increasing the shear rate at 25°C. This process was repeated twice in total, and the measurement results are presented below. Figure 4 middle.

[0124] Experimental Example 2 (1) Manufacturing of powder containing positive electrode material The positive electrode slurries prepared in Experimental Example 1 were vacuum dried at 130°C for 3 hours, then finely ground with a mortar and pestle, and then classified using a 250-mesh sieve to prepare powder containing positive electrode material from the slurry.

[0125] (2) Measurement of the calendered density of powder containing positive electrode material The 2 g powders prepared in (1) above were placed into a cylindrical metal mold inside a powder resistance meter (HPRM-1000, Hantech), and tested with 7 tons / 1.327 cm. 2 The surface pressure was applied. The height of the pressure die was measured using vernier calipers and used to calculate the calendering density. The results are shown in Table 2 below.

[0126] (3) Measurement of PSD of powder containing positive electrode material In the powder prepared in (1) above, the volumetric cumulative particle size distribution (PSD) of the powder containing the cathode material of Example 4 was obtained using a Microtrac S-3500. The obtained particle size distribution curve is shown below as data before calendering. Figure 1 middle.

[0127] For the powder containing the cathode material of Comparative Example 2, PSD was obtained in the same manner, and the data before calendering are shown below. Figure 2 middle.

[0128] Experimental Example 3 (1) Positive electrode slurry coating The positive electrode slurries prepared in Experimental Example 1 (1) were subjected to a concentration of 480 mg / 25 cm⁻¹. 2 The loading amount was coated onto a 15 μm thick aluminum film serving as the positive electrode current collector, and dried at 130°C to form the positive electrode active material layer. The thickness of the positive electrode active material layer was measured in this state and is listed in Table 2 below.

[0129] (2) Rolling For the slurry containing the positive electrode materials of Example 4 and Comparative Example 2, a positive electrode active material layer was coated on the positive electrode current collector as described in (1) above. Then, the calendering process was repeated until the porosity of the positive electrode active material layer was less than 30%. A graph showing the change in porosity of the positive electrode active material layer with the number of calendering cycles is shown in [the figure]. Figure 3 In this case, the porosity is calculated using the true density of the raw material after measuring the electrode thickness.

[0130] (3) Measurement of PSD at the positive electrode The cathode material (porosity: 28.3%) of Example 4, in which the porosity was adjusted to below 30% in (2) above, was heat-treated in a furnace at 700°C for 10 hours to collect cathode material. It was then finely ground using a mortar and pestle and graded using a 250-mesh sieve to obtain cathode material powder. The volumetric cumulative particle size distribution (PSD) of the obtained powder was obtained using a Microtrac S-3500. The obtained particle size distribution curve is shown as data after calendering. Figure 1 middle.

[0131] The PSD of the cathode (porosity: 29.4%) of Comparative Example 2 was obtained using the same method and is shown as data after calendering. Figure 2 middle.

[0132] [Table 2]

[0133] First, the results in Table 1 confirmed that, in the case of the slurry containing the cathode material of the examples, the solid content was 65% by weight or more and the viscosity was not more than 14,500 cP. This facilitated reducing the thickness of the cathode active material layer and made it easier to control the calendering process. The results confirmed that the calendering density of all examples was 2.9 g / cc or more.

[0134] On the other hand, it was confirmed that, compared with Examples 1 to 7, Comparative Example 1, which contained only lithium-rich manganese oxide corresponding to the first positive electrode active material, Comparative Example 2, which used a positive electrode active material in the form of secondary particles as the second positive electrode active material, and Comparative Example 3, in which the lithium-rich manganese oxide had a D50 of 6.7 μm and did not exhibit bimodal characteristics, exhibited lower solids content, higher viscosity, or lower rolling density under the same rolling conditions.

[0135] Furthermore, Comparative Example 2, which uses a secondary particle-form positive electrode active material as the second positive electrode active material, is compared with Example 4. Figure 1 and Figure 2It was confirmed that, compared to Comparative Example 2, the incidence of large particle breakage before and after calendering was very low in Example 4. Specifically, it was confirmed that the particle breakage rate of the first positive electrode active material according to Formula 1 was 14% in Example 4, but the particle breakage rate of the first positive electrode active material according to Formula 1 was 28% in Comparative Example 2.

[0136] On the other hand, reference Figure 3 It was confirmed that in Example 4, the porosity dropped below 30% even after only two calendering cycles, but in Comparative Example 2, the porosity only dropped below 30% after four calendering cycles.

[0137] In addition, refer to Figure 4 It was confirmed that the slurry obtained in Example 4 had a lower viscosity compared to Comparative Example 2.

[0138] On the other hand, observations were made on Examples 3 to 7, in which positive electrode active material A was used as the first positive electrode active material and positive electrode active material G was used as the second positive electrode active material, but only the ratio between the two was changed. It was confirmed that in Examples 3 to 5, where the weight ratio was set to 60:40 to 70:30, the solid content was 68% by weight and the viscosity was 14,500 cP or less, while ensuring a calendering density of 2.97 g / cc or more. Specifically, it was confirmed that in Examples 3 and 4, where the weight ratio was set to 60:40 to 65:35, the viscosity did not exceed 13,000 cP, the solid content was 68% by weight, and the calendering density was ensured to be 2.97 g / cc or more. Thus, along with the higher solid content and calendering density, low viscosity was also observed, thereby ensuring excellent processability.

Claims

1. A positive electrode material for a lithium secondary battery, the positive electrode material for the lithium secondary battery comprising: The first positive electrode active material contains a lithium-rich manganese oxide represented by the following chemical formula 1; and The second positive electrode active material has one or more particles and contains lithium transition metal oxide, wherein the particles are in the form of single particles composed of small pieces or quasi-single particles as a composite of fewer than 30 small pieces. The first positive electrode active material has a D50 of 8 μm or more, and has a larger D50 value than the second positive electrode active material. [Chemical Formula 1] Li 1+a [Mr 1-(b+c) Ni b M c ]O 2+d In chemical formula 1, M is selected from at least one of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.10≤a≤0.45, 0≤b≤0.5, 0≤c≤0.5, 0 <b+c≤0.5,0≤d≤1。 2. The positive electrode material for lithium secondary batteries according to claim 1, wherein: The cathode material exhibits a bimodal particle size distribution because the particle size distributions of the first cathode active material and the second cathode active material are different from each other.

3. The positive electrode material for lithium secondary batteries according to claim 1, wherein the first positive electrode active material is substantially free of cobalt.

4. The positive electrode material for lithium secondary batteries according to claim 1, wherein: The lithium transition metal oxide contained in the second positive electrode active material is represented by the following chemical formula 2 or chemical formula 3: [Chemical Formula 2] Li 1+p (Ni q Co r Mr s M 2 t )O2 In chemical formula 2, M 2 It is selected from at least one of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and -0.2≤p≤0.2,0.50≤q<1,0 <r≤0.40,0<s≤0.40,0≤t≤0.10,q+r+s+t=1, [Chemical Formula 3] Li 1+w [Mr 1-(x+y) Ni x M 3 y ]O 2+z In chemical formula 3, M 3 It is selected from at least one of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0 <w,0≤x≤0.5,0≤y≤0.5,0<x+y≤0.5,0≤z≤1。 5. The positive electrode material for lithium secondary batteries according to claim 4, wherein: The lithium transition metal oxide contained in the second positive electrode active material is represented by chemical formula 2, wherein q, r, s, and t satisfy 0.60 ≤ q < 1, 0 < t, and t, respectively. <r≤0.30、0<s≤0.30、0≤t≤0.10。 6. The positive electrode material for lithium secondary batteries according to claim 1, wherein: In chemical formula 1, b and c satisfy 0.1 ≤ b + c ≤ 0.

45.

7. The positive electrode material for lithium secondary batteries according to claim 1, wherein: The first positive electrode active material and the second positive electrode active material are contained in a weight ratio of 90:10 to 60:

40.

8. The positive electrode material for lithium secondary batteries according to claim 1, wherein: The D50 of the first positive electrode active material is 8 μm to 15 μm.

9. The positive electrode material for lithium secondary batteries according to claim 1, wherein: The D50 of the second positive electrode active material is 2 μm to 5 μm.

10. The positive electrode material for lithium secondary batteries according to claim 1, wherein: The BET specific surface area of ​​the first positive electrode active material is 1.3 m². 2 / g to 4.0 m 2 / g.

11. The positive electrode material for lithium secondary batteries according to claim 1, wherein: The first positive electrode active material has a crystal structure in which layered phase and rock salt phase are mixed.

12. The positive electrode material for lithium secondary batteries according to claim 1, wherein: The first positive electrode active material has a two-phase crystal structure represented by the following chemical formula 1a: [Chemical Formula 1a] A·Li2MnO3·(1-A)·Li[Ni 1-n-m Mr n M m ]O2 In chemical formula 1a, M includes at least one selected from Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.10≤A≤0.45, 0.4≤n<1, 0≤m≤0.

2.

13. The positive electrode material for lithium secondary batteries according to claim 1, wherein: The particle fragmentation rate of the first positive electrode active material, according to the following mathematical formula 1, is less than 20%: [Mathematical Expression 1] The particle fragmentation rate (%) of the first positive electrode active material = the particle distribution ratio at the maximum peak obtained from the PSD (volume cumulative particle size distribution) of the positive electrode material before rolling (%) - the particle distribution ratio at the maximum peak obtained from the PSD of the positive electrode material after rolling (%) In mathematical formula 1, The PSD of the cathode material before calendering refers to the PSD of the powder obtained by drying and pulverizing the cathode slurry containing the cathode material. The PSD of the calendered cathode material refers to the PSD of the cathode material powder recovered from the cathode containing the cathode material and having a porosity of less than 30%.

14. A positive electrode slurry for a lithium secondary battery, the positive electrode slurry comprising: a positive electrode material, a binder, a conductive material, and a solvent as described in any one of claims 1 to 13.

15. The positive electrode slurry for lithium secondary batteries according to claim 14, wherein: The cathode slurry has a solids content of 65% or more relative to the total weight of the cathode slurry and a viscosity of 14,500 cP or less.

16. A positive electrode for a lithium secondary battery, the positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer disposed on the positive electrode current collector and comprising a positive electrode material. The positive electrode material comprises: The first positive electrode active material contains a lithium-rich manganese oxide represented by the following chemical formula 1; and The second positive electrode active material has one or more particles and contains lithium transition metal oxide, wherein the particles are in the form of single particles composed of small pieces or quasi-single particles as a composite of fewer than 30 small pieces. The first positive electrode active material has a D50 of 8 μm or more and a larger D50 value than the second positive electrode active material. [Chemical Formula 1] Li 1+a [Mr 1-(b+c) Ni b M c ]O 2+d In chemical formula 1, M is selected from at least one of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.10≤a≤0.45, 0≤b≤0.5, 0≤c≤0.5, 0 <b+c≤0.5,0≤d≤1。 17. The positive electrode for a lithium secondary battery according to claim 16, wherein: When pressurized to 7 tons / 1.327 cm at room temperature 2 At that time, the calendering density was above 2.9 g / cc.

18. The positive electrode for a lithium secondary battery according to claim 16, wherein: The loading capacity was 420 mg / 25 cm. 2 Up to 540 mg / 25 cm 2 .

19. A lithium secondary battery comprising the positive electrode for a lithium secondary battery as described in claim 16.

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